Phase Transformation of Micrometer-Sized Mn-Al-C

Mn54Al46C2.44 alloy as new permanent magnetic materials was produced by induction melting, and its powders were produced by low energy ball milling. The milled powders were annealed to study the effect on their phase transformation and magnetic properties. The powder undergoes massive phase transformation at an annealing temperature of 450 degrees C, and reaches the maximum saturation magnetization (sigma(s)) when annealed at 480 degrees C for 5 min, while its intrinsic coercivity (H-ci) continually increases with the temperature. The initial increment of the H-ci is due to the phase transformation from paramagnetic epsilon-phase to ferromagnetic tau-phase and remaining epsilon-phase and formation of secondary phases, such as nonmagnetic gamma(2)-and beta-phases, that acts as pinning points for the domain walls. The next one is caused by the increasing percentage of the secondary phases that decreases sigma(s). Based on the delta M analysis, it can be verified that the increased H-ci with increasing secondary phases when annealed at temperatures above 480 degrees C is due to the decreasing magnetization.